I'm going to go with something that is scary because it was apparently mundane. When I took an intro to archeology course for medievalists the instructor who had many years of medieval digs under her belt said that they were used to digging up cemeteries, and not usually much affected by it, but that you would occasionally find people who by their poses had apparently been buried alive and woken up and struggled before dying for real. This was common enough that it was not totally surprising, though it could never be common enough for you to get used to it.